The speed of the ASUS XG-C100C network card is not strictly limited by the motherboard's maximum PCI Express speed, but it does depend on the available PCI Express lanes and their version.

- The XG-C100C uses a PCI Express 3.0 x4 interface, which means it requires four PCI Express lanes to operate at its full potential of 10Gbps.
- If the motherboard only supports PCI Express 2.0 or has fewer available lanes, the card's performance might be affected. However, the card is designed to be backward compatible with older PCI Express versions (PCI Express 2.0 and 2.1), although the maximum speed may be reduced accordingly.

In summary, while the card can function with lower PCI Express versions or fewer lanes, its full 10Gbps speed is optimized when used with a motherboard that supports PCI Express 3.0 x4.